Why is extensive oil flushing required when retrofitting to HFC refrigerants?

Extensive oil flushing is essential when retrofitting to HFC refrigerants primarily to ensure the system operates correctly and efficiently with the new refrigerant.

Firstly, HFC refrigerants differ significantly in their chemical properties compared to older refrigerants like CFCs. If any residual CFC or mineral oil remains in the system, it can lead to compatibility issues, resulting in poor performance or even damage to the system. The compatibility of lubricants is critical because HFCs, typically designed to operate with polyol ester (POE) oils or similar synthetic oils, may not mix well with mineral oils used in older systems. This incompatibility can reduce the effectiveness of lubrication in the compressor, ultimately leading to failure.

Moreover, cleaning the compressor thoroughly through flushing is crucial to prevent any contaminants that could impact the system's reliability from affecting the operation. Residual oil can cause the new refrigerant to degrade, leading to decreased efficiency and increased wear on components.

Each of these points reinforces the need for a comprehensive flushing process during the retrofit, making the choice that includes all specified reasons the most accurate.